1. Field of the Invention
This invention concerns the field of non-metallic pulleys, and, specifically, the field of boss mounted, non-metallic pulleys particularly adapted for use in industrial applications, such as automotive, aviation, appliances and the like.
2. Description of the Prior Art
In recent years, the use of newer, non-metallic materials for various automotive components has become increasingly widespread. In order to remain competitive in the world market and in response to Federal mandates, automobile manufacturers have striven to achieve better and better fleet fuel economy ratings. One of the most obvious and most common ways to improve fleet miles per gallon ratings is by reducing weight. Generally, reducing the weight of an automobile necessitates replacing heavy metal components with those fabricated of lighter materials.
While metallic components suffer the disadvantage of being relatively heavy, the performance characteristics of metals are such that they are not always easy to duplicate with non-metallic materials. Particularly, it is difficult to duplicate the inherent strength properties of metal in non-metallic materials such as plastics without incorporating design modifications to the application. Furthermore, much care must be given to the particular type of plastic selected.
One non-metallic material, presently used for automotive pulley applications, is a type of thermoset phenolic molding compound. It is sold under the trade name "Durez" thermoset and is available from the Occidental Chemical Corporation. Phenolic molding compound, when used in pulley applications, enjoys a weight advantage over a typical metal, such as spun steel, of approximately 2:1. Its material characteristics with regard to wear resistance, heat resistance, dimensional stability, compressive strength and impact strength have been shown to be compatible with use in fabricating automotive pulleys.
One problem has arisen with the use of non-metallic automotive pulleys formed of phenolic molding compound. Heretofore, the use of this material has been limited to pulleys having a minimal mounting offset. The term mounting offset refers to the distance between the face of the pulley's mounting flange or hub and the center of the pulley belt. The longer the distance between the mounting flange and the center of the belt, the greater is the mounting offset and the greater the stress placed on the pulley belt due to the effect of the cantilevered load.
A problem arises because certain prior art automotive engine pulleys, such as those used on the crankshaft, typically require a relatively large mounting offset. That is, these pulleys must be mounted such that there is a large distance between the center of the pulley belt and the location of the mounting surface.
What is needed is a non-metallic pulley which may be used for applications which require a substantial mounting offset in the hub mounted pulley, but which will still exhibit enough strength to support the heavy, cantilever load applied by the pulley belt.